Tru64 will give you the best experience of the time, allow you to use the GEM compilers, TruClusters, and all of hte interesting layered products.  The issue is license managers as Nelson says, but Internet search is your friend i.e. different unlimited time styles license PAKs for Tru64 have been reported to have been seen in the wild, however YMMV.

On Sat, Sep 19, 2020 at 12:27 AM Nelson H. F. Beebe <beebe@math.utah.edu> wrote:
>> I have an opportunity to buy a DEC AlphaServer. Is there a version of Unix
>> which will run on this?

There are several Debian Alpha ISO images available:

        http://archive.debian.org/debian/dists/etch/main/installer-alpha
        https://cdimage.debian.org/cdimage/archive/5.0.10/alpha/iso-cd
        https://cdimage.debian.org/cdimage/ports/2020-08-19/
        https://wiki.qemu.org/Documentation/Platforms/Alpha
        https://www.debian.org/ports/alpha/
        https://www.debian.org/releases/woody/alpha

And Gentoo Linux:

        https://wiki.gentoo.org/wiki/Alpha/FAQ

There is also NetBSD:

        https://cdn.netbsd.org/pub/NetBSD/NetBSD-9.0/alpha

And OpenBSD:

        http://www.openbsd.org/alpha.html

And FreeBSD:

        https://www.freebsd.org/releases/6.0R/hardware-alpha.html

We ran DEC OSF/1 until the power supplies on our several Alpha systems
died, but it had an annual license fee, and the O/S shutdown when the
license expired.

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- Nelson H. F. Beebe                    Tel: +1 801 581 5254                  -
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